Degradation of triclosan in a peroxymonosulfate/Br− system: Identification of reactive species and formation of halogenated byproducts

Peroxymonosulfate (PMS), a widely used in situ chemical oxidation agent, has attracted increasing attention in ground water/soil remediation. PMS is relatively stable with lifetime from months to even years in subsurface. The residual PMS can react with various of organics or inorganics species in environment, which may pose long term environmental effects. In this study, reaction between PMS and bromide (Br − ) in water, and thus to the transformation of triclosan (TCS), an antibiotic agent, was studied. We found that TCS cannot be degraded by PMS alone but was efficiently removed in the presence of both PMS and Br − . This was due to the formation of free bromine upon the oxidation of Br − by PMS. Formation of bromine radical (Br ) in PMS/Br − system was unlikely according to quenching tests. Reaction between free bromine and TCS generated brominated TCS intermediates which underwent further degradation to brominated disinfection byproducts (DBPs), of which bromoform (CHBr 3 ) and dibromoacetic acid (DBAA) were the most prominent ones. Their yields reached 1.31 µM and 0.49 µM in 24 h, respectively, when 1 mg/L TCS was treated with 100 µM PMS and 100 µM Br − . Presence of humic acid (HA) remarkably enhanced the formation of monobromoacetic acid (MBAA), DBAA, and bromochloroacetic acid (BCAA) but inhibited the formation of CHBr 3 and dibromochloromethane (CHClBr 2 ). Thus, even though certain phenolic contaminants like TCS can be effectively removed in PMS/Br − system, formation of free bromine and DBPs makes it not a good treatment strategy. Particular attention should be paid when Br − is presented in PMS-based oxidation process.